Michael Frayn's play is a cerebral and, at times, poetic piece, an exploration of scientific responsibility which is based on a true story.

In 1941 Werner Heisenberg, the pre-eminent nuclear scientist, left his native Germany to visit occupied Norway. While there, he met with his old mentor, Niels Bohr, and his wife, Margrethe, at their home.

It is known the two men took a long walk, at the end of which, they parted in anger. What was said during their conversation was never revealed and this play is Frayn's speculation.

It is cleverly constructed with several versions of what happened unfolding and being enacted by the three protagonists looking back and trying to recall the event.

Was it merely to reminisce about their early days together when they developed their theories: Was it to discuss morality or was it to elicit advice on harnessing atomic energy for use as a weapon?

The play has strands of gentle humour amid the serious debate and the quality of the writing is matched by tremendous performances from the three actors.

Gary Blair (as Bohr) is all smiling bonhomie until provoked into anger, John Adam (Heisenberg) is forever apologising for the Nazi occupation.

It falls to Margrethe, played with the right degree of cool restraint by Eleanor Gamper, to act as the outside observer and commentator, adjudicating and correcting where necessary any faulty recall that the men make.

Runs until September 25